Electrical and electronic fuses are well-known in the art of circuit protection. Some of these fuses can be made of one or two pieces, whereas others must be made of many pieces. Larger fuses that accommodate larger voltage or current ratings tend to need and have many pieces.
FIG. 1 shows a prior art fusible link-containing structure 10 for an electrical fuse. Such prior art fusible links are used in semiconductor fuses, such as the L15S, L25S, and L50S semiconductor fuses available from Littelfuse, Inc., Des Plaines, Ill. The fusible link-containing structure 10 includes a metallic element 12 having a portion 14 of reduced cross-section. The reduced cross-section is typically, but not exclusively, formed by punching two lines of holes 16, 18 in the metallic element 12. The fusible link 20 results from and is formed by the holes 16, 18 in this portion 14 of reduced cross-section.
The prior art structure also includes at least one arc-quenching tab secured to the metallic element at a position spaced apart from the fusible link 20. As may be seen in FIG. 1, the prior art structure shown includes two such tabs 22 and 24, with each tab 22 and 24 being made of two strips of a pre-cured (i.e., hardened) insulating material. The pre-cured tabs 22 and 24 are secured to the metallic element 12 by means of mechanical fasteners. In the embodiment of FIG. 1, the mechanical fasteners are rivets 26, 28, 30, and 32, and the tabs 22 and 24 are made of a pre-cured melamine material. As may be seen in FIG. 1, the rivets 26, 28, 30, and 32 do not puncture the metallic element 12. Rather, they puncture only the pre-cured tabs 22 and 24, at a position relatively near the ends; 34, 36, 38, and 40 of those tabs.
One or more of these prior art structures 10 are typically inserted into a cylindrical fuse body. If several of these prior art structures 10 are used in a cylindrical fuse body, they extend radially around the lengthwise axis within that fuse body.
Although the prior art structures 10 of FIG. 1 are generally well-suited for their intended purposes, it was determined that those prior art structures 10 had certain limitations that needed to be addressed. First, as can be seen in FIG. 1, the size of the rivets 26, 28, 30, and 32 requires that the ends 34, 36, 38, and 40 of the tabs 22 and 24 extend a relatively large distance away from the top 42 and bottom 44 of the metallic element 12. In fact, the total width of the structure 10, including the solid melamine tabs 22 and 24, will be approximately 5/8". As a result, the fusible-link containing structure 10 with those outwardly extending tabs 22 and 24 will require a fuse housing that has a larger diameter than would otherwise be necessary.
Second, when the tabs 22 and 24 are riveted in place over the metallic element 12 to provide the friction fit shown in FIG. 1, there are inevitably gaps 46 between the pre-cured tabs 22 and 24 and the fusible link-containing structure 10. These gaps 46 lead to several problems. One problem is that the gaps 46 can provide a space through which an arc can travel. As a result of these gaps 46, the arc-quenching role of these pre-cured tabs 22 and 24 could be fully or at least partially defeated. Another problem is that the pre-cured tabs 22 and 24 fit relatively loosely on the metallic element 12. As a result, or perhaps upon further loosening of the rivets, there could be relative movement between the tabs 22 and 24 and the metallic element 12. The friction-fit tabs 22 and 24 could still shift outwardly along the axis of the metallic element 12, and towards the ends of that element 12. If the tabs 22 and 24 shifted a sufficient distance outwardly, one or both of the tabs 22 and 24 could obscure one or both lateral ends of the metallic element 12, making it impossible to solder or otherwise connect the ends of the metallic element 12 to the other circuit elements (for example, the end caps) in the fuse.
A further problem arises as a result of the inherent nature and functions of a fuse. When a fuse is placed within an electrical circuit, it is de signed to protect that circuit against short circuit conditions. Prior to the opening of the fuse link during such short circuit conditions, the metallic element 12 is typically heated to a high temperature. Some of the heat generated by the fuse element 12 heats the rivets of the fusible link-containing structure 10 of FIG. 1. These heated rivets are in close proximity to the cylindrical housing, and there is no sand or other similar insulator between the rivet and body inner wall. As a result of this proximity, under 300% current overload or other similar extreme conditions, the rivets can melt. Such melting rivets heat the adjacent fuse housing, and melt, char, or form a hole in that housing.
These characteristics of the prior art fuse link-containing structures suggest the merit of an improved structure.